voice scrambler
Andy,
Klug is right,
The simplest way is to build a spectrum inverter.
You'll need a generator, above the audio spectrum, for example at FG=3.3kHz. This generator must be multiplied with your microphone AF ( FA=(0.3 to 3kHz), it can be done with the aid of a frequency mixer. As a result you will have two products : (FG+FA) and (FG-FA). The sum product is above 3kHz and is unusable, because you can't pass this product via a walkie-talkie, and must be filtered by a 3kHz low-pass filter. After the LPF you will find your AF inverted - low frequencies are on the high end and vice versa. On receive, above mixing and filtering must be done again to recover original AF.
This way of scrambling is not effective, it is very easy to intercept such a signal, but is very simple and cheap.
If you need something more complicated, take a look at CML site and search for IC's, referenced by Klug.
Give me (PM me) your e-mail address. I'll post you an example schematic.
STOYANOV
PS: Klug, 73 from LZ land.